Interpretive Summary: Melaleuca quinquenervia is a serious wetland weed from Australia that threatens the Everglades ecosystem. Classical biological control programs have resulted in a fundamental change in the biology of the tree, whereby it now produces much less seed because of extensive herbivory by introduced, host-specific insects. Seed rain is much reduced and, coupled with naturally high mortality of seedlings, populations are not recruited and replaced at the same densities as before the introduction of biological control agents. As a consequence the plant now appears to be less invasive and, therefore, less damaging to important natural areas.

Technical Abstract:
Although the exotic invasive tree Melaleuca quinquenervia has invaded and dominated South Florida wetlands since its introduction in 1886, its formerly unfettered seed production is now constrained by intentionally introduced herbivores, especially Oxyops vitiosa Pascoe (Coleoptera: Curculionidae). We examined the recruitment and mortality of M. quinquenervia seedlings in this new herbivory context over a 3-y period in a seasonally inundated wetland. Four distinct water regimes characterized this site: dry, dry to wet transition, flooded, and wet to dry transition. A mean of 0.2 (+ 0.03) viable seeds m-2 d-1 fell into the plots with recruitment highest in the dry to wet transition and lowest in the flooded water regime. Seedlings that emerged during the transition from the dry to wet regime were often smothered by algae during the following flooded water regime unless their height exceeded the water depth. The mean estimate of population growth (') was 0.64 + 0.05 indicating negative population growth. The original density of 64.8 (+ 4.5) seedlings/saplings m-1 was eventually replaced by 0.5 (+ 0.2) seedlings/saplings m-1 after three years, a 99.2% population reduction. Elimination of introduced insect herbivores using insecticides did not reduce mortality of M. quinquenervia seedlings/saplings. The study documented a change in the invasion trajectory M. quinquenervia that was likely caused by reduced seed inputs from aerial seed banks depleted by insect herbivory. This may presage a fundamental alteration of its population dynamics, perhaps transforming it into a less invasive and, therefore, less ecologically damaging species.